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Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 181433
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1033 AM EDT Thu Apr 18 2024

.SYNOPSIS...
A slow moving warm front will exit the local area this morning
while a weak cold front tracks through later today. High
pressure briefly builds in before a stronger cold front pushes
across the region Friday evening into the night. High pressure
returns late in the weekend into early next week.

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --Mid morning update: A nearly stationary boundary stretches
north to south from north-central MD down to southern Maryland
this morning. To the east of the boundary, winds are out of the
east, allowing low clouds/fog remain to remain in place over
northeastern Maryland. To the west of the boundary, winds are
out of the west, allowing low clouds to clear out. Some
additional stratocumulus is developing to the west of the
boundary as mixing deepens from western MD into the DC Metro.
This aforementioned boundary is expected to show little movement
throughout the day, and could lead to a sharp temperature
gradient between northeast Maryland and the DC metro. A few
sprinkles could also be possible this afternoon across northeast
Maryland in the vicinity of the boundary where low-level
convergence will be maximized. Previous discussion follows...

Gusts up to 15 to perhaps 20 mph are possible during the
afternoon hours as the boundary layer becomes better mixed. The
net downsloping effect behind this front will yield a warm mid-
April day across the Mid-Atlantic. As 850-mb temperatures rise
into the 10 to 12C range, dry adiabatic mixing would yield upper
70s to low 80s. This is indeed the forecast for the D.C. metro
down into central Virginia as well as the Shenandoah Valley. The
cooler spots will be over the Allegheny Front and northeastern
Maryland where highs remain in the mid/upper 60s.

By this evening and into the night, winds continue to back with
a resulting east-northeasterly flow. This onshore flow regime
allows for a return of marine stratus to the forecast area. A
cool and damp wind will yield a cooler night than previous days.
Forecast lows are mainly in the mid/upper 40s, with some low 50s
across the I-64 corridor and in the Allegheny mountain valleys.
Any shower chances are expected to hold off until after sunrise
on Friday.-- End Changed Discussion --

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
An expansive upper trough extending across southern Canada into
the Great Lakes region will support a pattern change into the
upcoming weekend. Warm advection ahead of the attendant cold
front will yield periods of showers on Friday. Total rainfall
amounts are not terribly impressive, generally running around
0.10 inches, locally up to 0.25 inches in the higher terrain.
This is accompanied by a slight chance for thunderstorms,
especially west of I-95. Despite mainly south to southeasterly
flow, the mostly cloudy skies should keep temperatures down
relative to Thursday. Those east of U.S. 15 will likely stay in
the mid/upper 60s (locally a bit cooler in northeastern
Maryland), with slightly warmer conditions to the west outside
of mountain locales. Shower chances gradually come to an end
from west to east overnight. Nighttime lows will range from the
40s over the mountains and along the Mason-Dixon Line, to
low/mid 50s elsewhere.

Aside from a few lingering showers early Saturday morning over
far southern Maryland, expect a dry day over the region on
Saturday. Temperatures stay slightly above normal owing to a
downsloping northwesterly wind. However, this round of winds
should be much stronger than recent frontal passages. The latest
forecast package calls for afternoon gusts of 20 to 30 mph,
locally up to 35 to 40 mph along the Allegheny ridgetops. Some
residual wind lingers into the overnight hours which will make
for a chilly Saturday night. Forecast low temperatures range
from the upper 30s to mid 40s, with near freezing conditions
along the Allegheny Front.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A front will be draped along the southeastern states Sunday while
high pressure extends eastward from the Plains to its north. Low
pressure will be tracking along the front, spreading rain toward
southern Virginia by Sunday evening. Model consensus continues to
indicate rain will largely remain south of the forecast area, but
there are still some 20-30 PoPs across southern zones. Even without
the rain, Sunday will be a mostly cloudy and cooler day. Clouds will
depart late Sunday night. Some valleys west of the Blue Ridge could
drop into the mid 30s should skies clear and winds become light,
which would pose a risk for frost.

The surface high will move closer on Monday, although there will be
a compact short wave trough (or even closed low) overhead. While
some extra clouds are possible, the chance for rain is currently
low. Temperatures will be near or slightly below normal.

The high will remain in control to start Tuesday, and southerly
return flow will result in a warm up. The next trough and associated
cold front will approach late Tuesday into early Wednesday. Moisture
may be limited, resulting in the highest shower chances along the
Appalachians. Instability will also be limited, so thunderstorms
appear unlikely. Shower chances linger into Wednesday to account for
slower solutions. Otherwise, expect gusty winds and cooler
temperatures behind the front as strong high pressure builds in from
the northwest.

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
A wavy stationary front currently extends from the Carroll
County in north-central Maryland down toward Calvert County in
southern Maryland. To the east of this boundary, a thick marine
stratus deck has formed which is impacting KBWI and KMTN with
IFR ceilings. This IFR deck has remained stubborn, and may take
into the afternoon to ultimately mix out. Winds may hold out of
the east to the east of this boundary through much of the day,
while winds remain northwesterly to the west of the front with
some gusts up to 15 knots or so. Heading into the evening and
nighttime, winds back over to east- northeasterly which favors
another round of low stratus. MVFR to IFR ceilings become likely
late tonight into Friday.

Rain showers return to the forecast on Friday, accompanied by
some slight thunder chances for the more western terminals.
Restrictions are expected to persist with MVFR ceilings
remaining for portions of the day. A stronger cold front tracks
through late Friday which should allow for a return to VFR
conditions on Saturday. A gusty northwesterly wind is expected
with forecast gusts up to 20 to 25 knots.

VFR conditions and winds AOB 10 kt are most likely for Sunday and
Monday. Effects from low pressure will likely remain south of the
area, but rain could near CHO Sunday evening.-- End Changed Discussion --

.MARINE...
Wind fields across the waterways picked up earlier in response
to a southeastward propagating outflow boundary. However, its
influence has waned with below advisory winds being observed. A
weak cold front pushes across the waters today which could bring
near 18 knot gusts at times. Eventually a shift to east-
northeasterlies is expected with another uptick in winds,
particularly over the northern Chesapeake Bay. Some 20 knots
gusts are possible as this occurs later this evening.

Rain showers are in the forecast on Friday, although the main
thunder chances should stay west of the tidal Potomac and
Chesapeake Bay. However, these details could change so check
back for the latest forecasts. A stronger cold front arrives
late Friday night into early Saturday. This leads to a
strengthening northwesterly wind and likely Small Craft
Advisories for Saturday and possibly into the night.

Overall winds will lessen Sunday, but some gusts may approach
advisory criteria. Sub-SCA conditions are likely Sunday night and
Monday as high pressure builds in from the west.

.TIDES/COASTAL FLOODING...
-- Changed Discussion --Tidal anomalies will hold steady or trend down slightly today with a
brief period of northerly winds. Easterly winds develop tonight then
become southerly Friday, which will result in rising anomalies. The
greatest chance for minor flooding will be along sensitive shoreline
(Annapolis, Straits Point, DC SW Waterfront) with the Friday and
Friday night high tides, although it may be close in other
locations. Water levels will drop southerly in gusty northwest
postfrontal flow.-- End Changed Discussion --

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to midnight EDT
tonight for ANZ530>533-538>542.
Small Craft Advisory from 8 PM this evening to 2 AM EDT Friday
for ANZ534-537-543.-- End Changed Discussion --

SYNOPSIS...BRO
NEAR TERM...BRO/KJP
SHORT TERM...BRO
LONG TERM...ADS
AVIATION...ADS/BRO
MARINE...ADS/BRO
TIDES/COASTAL FLOODING...ADS

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